Although applicable in principal to any system that is used to jam wireless signals, the present invention and its underlying problem will be hereinafter described in combination with FHSS jammers.
In frequency-hopping spread spectrum or FHSS system, radio signals are transmitted by rapidly switching a carrier among many frequency channels. The switching of the frequency channels is usually based in a pseudorandom sequence known to both transmitter and receiver. FHSS systems therefore spread their signal over rapidly changing frequencies. An available frequency band may e.g. be divided into sub-frequencies. The emitted signals may then rapidly change or hop among these sub-frequencies in a pre-determined order.
FHSS signals are e.g. used in first generation WLAN systems, in Bluetooth systems and especially in the free 2.4 GHZ frequency spectrum e.g. by radio control devices for model vehicles, like e.g. aircraft and drones.
Especially the application of FHSS modulation to remote controlled drones and aircraft may pose a problem in situations or areas that do not allow flying such aircraft or drones. It may for example be prohibited to fly model aircraft or drones near an airport for safety reasons. With other modulation methods, the emitter or controller signals may easily be jammed, since the relevant frequencies are known. However, with FHSS modulating transmitters, it is difficult to track the relevant emissions.
To jam such FHSS signals e.g. of model drones, the full frequency spectrum may therefore be jammed. This however also blocks the frequency spectrum for any other use. If only the relevant sections of the frequency band may be jammed, a so called predictive following jammer may be used that anticipates and follows the frequency hops and only jams the relevant frequencies. However, with predictive following jammers it is necessary to know the exact frequency sequence and timing of the frequency hops.